Simple Underground Starter iron farm

A cheap iron farm for three villagers and one zombie that fits in a 30x30 area. The villagers sleep in a small chamber with the zombie in a boat, and the golems drop into a lava blade over a single hopper. It is a handful of slabs, fences and buckets with no redstone, and it can be repeated on the opposite side of the pit for more output. Java only.

Line the boat up exactly as shown. The three slabs are there because of it, and if the boat is off, light gets through and the zombie burns. Bottom half slabs right above the box fix it if you cannot align it.
Golems spawning outside the pit means the size or the facing is wrong. One builder needed an extra row of path blocks on three sides.
If the villagers suffocate in the morning, the blocks above the empty space beside the bed are placed wrong.
Lightning turns villagers into witches and kills the farm overnight. Put a lightning rod somewhere safe nearby.
The creator says the boat stops the zombie despawning, but two builders lost theirs anyway. Name tag it, or use a zombie that can pick up items.
It scales. Move 32 blocks out from the hole and repeat the box on the opposite side, one builder runs four of them.